pancuronium and dimethyltubocurarine

We recently demonstrated that conserved tyrosines Tyr198 of the alpha subunit and Tyr117 of the gamma subunit of the acetylcholine receptor stabilize binding of the curariform antagonist dimethyl-d-tubocurarine (DMT). To test the hypothesis that DMT interacts directly with these tyrosines, and therefore bridges the alpha-gamma subunit interface, we introduced point mutations into these key positions and expressed one or both mutant subunits in alpha 2 beta gamma 2 acetylcholine receptors in 293 HEK cells. Binding of DMT, measured by competition against the initial rate of 125I-alpha-bungarotoxin binding, shows high affinity for aromatic mutations, reduced affinity for polar mutations, and lowest affinity for arginine mutations. Similar side chain dependences were observed for both Tyr alpha 198 and Tyr gamma 117, indicating interaction of these residues with two symmetrical chemical groups in DMT. Two more bisquaternary antagonists, pancuronium and gallamine, show side chain dependences similar to that of DMT, indicating that the primary stabilizing interactions are aromatic-quaternary in both subunits. For the rigid ligands DMT and pancuronium, co-expressing mutant alpha and gamma subunits revealed independent contributions by each determinant, but strict independence was not observed for the flexible ligand gallamine. The free energy contributed by each aromatic-quaternary interaction was estimated to be 2-4 kcal/mol, as determined from the free energy difference between aromatic and alkyl hydroxyl mutations. Our results suggest that bis-quaternary competitive antagonists bridge the alpha-gamma subunit interface by fitting into a pocket bounded by tyrosines at positions 198 of the alpha subunit and 117 of the gamma subunit.

Topics: Animals; Bungarotoxins; Cholinergic Antagonists; Gallamine Triethiodide; Mice; Pancuronium; Receptors, Cholinergic; Structure-Activity Relationship; Tubocurarine

The neuromuscular effects of the combined administration of pancuronium and dimethyltubocurarine were evaluated in children undergoing reconstructive surgery (n = 6), or the skin grafting of acute burn wounds: body surface area (BSA) burns less than 40% (n = 5); and BSA burns greater than 40% (n = 6). A dose of pancuronium 0.005 mg kg-1 was considered to be equipotent with dimethyltubocurarine 0.02 mg kg-1, and each dose was defined as being equal to 1 relaxant equivalent (RE). Incremental doses of the combination of pancuronium and dimethyltubocurarine were administered until a 95% depression of twitch height was achieved (ED95). These results were compared with previously published data for pancuronium and dimethyltubocurarine alone. The mean ED95 of the combination in the control population (reconstructive surgery) was 5.1 RE, compared with 10.8 RE and 10.0 RE for pancuronium and dimethyltubocurarine , respectively, administered alone. In the acutely burned population, the mean ED95 for the combination was 9.9 and 15.9 RE, respectively, compared with 26 RE for pancuronium alone in burned patients. In all groups of patients, significantly less total drug was required when the combined therapy was used.

Topics: Burns; Child; Dose-Response Relationship, Drug; Drug Synergism; Humans; Muscle Contraction; Neuromuscular Blocking Agents; Neuromuscular Junction; Pancuronium; Surgery, Plastic; Synaptic Transmission; Tubocurarine